For that part of the lab you're supposed to be making the edit to the Repo that's stored up on GitHub, using GitHub's web interface, rather than using the Git Bash commands on your laptop.
To do the commit on the GitHub website, you click on the README.md file, then click on the little pencil icon, and then make your change, and scroll down to the bottom to put in your commit message at the place where it says "Update Readme.md" in a textbox in light gray.
Hope that helps!